1. Field of the Invention
The present invention relates to a charged particle beam apparatus which irradiates charged particles like ions, a method for controlling charged particles, and a frequency adjustment apparatus. Particularly, the present invention relates to a charged particle beam apparatus, a method for controlling charged particles, and a frequency adjustment apparatus, which are capable of independently controlling a plurality of charged particle beams.
2. Description of the Related Art
The resonance frequency of a crystal resonator which is a typical piezoelectric device is determined by the thickness of a crystal piece and the film thickness of a metal electrode formed on the top surface thereof. Conventionally, to acquire a desired resonance frequency of a crystal resonator, processes of i) cutting out a crystal piece to a specified thickness, ii) polishing the top surface thereof, and forming a metal film electrode to be a base on the top surface by sputtering deposition or the like, and iii) adjusting the thickness of the metal electrode film while measuring the resonance frequency are performed. As a method of adjusting the thickness of a metal electrode film, there is a method known which irradiates an ion beam from an ion gun to etch the metal electrode film to make the metal electrode film thinner. The ion-beam-etching based frequency adjusting scheme is disclosed in, for example, Unexamined Japanese Patent Application KOKAI Publication No. 2000-323442 and Unexamined Japanese Patent Application KOKAI Publication No. 2003-298374.
A conventional ion gun for frequency adjustment comprises a main body 811, an node 812, a filament 813, a gas inlet 814, a screen grid 815, an accelerator grid 816 and a plurality of DC power supplies, as shown in FIG. 12.
With such a configuration, an Ar gas, for example, as a discharge gas is supplied into the main body 811 from the gas inlet 814, the filament 813 is energized to be heated so that Ar plasma is generated by DC hot cathode discharge between the filament 813 and the anode 812, a high voltage is applied to the accelerator grid 816 from a high-voltage power supply to generate a voltage gradient in a direction of accelerating ions, and positive Ar ions are ejected as an ion beam which is irradiated to a crystal resonator 821 mounted on a mount table 822.
The screen grid 815 and the accelerator grid 816 have pluralities of apertures (draw ports).
When a group of apertures is formed in a pattern as shown in FIG. 13, a single ion beam having an ion current density distribution which is most intense at the center and gradually becomes weaker toward a periphery as shown in FIG. 14 is formed. FIG. 14 shows the ion current density at the position of a substrate to be etched, and represents a distance from a position facing the center of the ion gun as an origin.
Recently, to reduce the space of the apparatus and shorten the process time, a plurality of crystal resonators are processed by irradiating a plurality of ion beams having an ion current density distribution as shown in FIG. 17 to a plurality of piezoelectric devices from a single ion gun. FIG. 17 shows the ion current density at the position of a substrate to be etched, and represents a distance from a position facing the center of the ion gun as an origin.
As shown in FIG. 15, the basic configuration of the ion gun which irradiates a plurality of ion beams is identical to that of the single-ion-beam ion gun shown in FIG. 12. It is to be noted however that as shown in FIG. 16, the screen grid 815 and the accelerator grid 816 in which plural groups of apertures (two in the diagram) are formed are disposed to generate a plurality of ion beams.